Gas flushing device for metallurgical melting pots

ABSTRACT

The invention relates to a gas flushing device for metallurgical melting pots, having the following construction: a porous plug is arranged in an upper cylindrical housing at the gas outlet end thereof and in a lower cylindrical housing on the adjacent section thereof, an annular chamber is provided at least between the lower housing and the porous plug which is filled with a mass, whereby the porous plug, housings and mass are made from a refractory ceramic material.

The invention pertains to a gas purging device for metallurgical meltingvessels. Numerous variations of gas purging devices as well ascorresponding gas purging elements, particularly gas purging plugs, havebeen known and used for many years.

Discrete gas purging plugs can be realized with so-called directional ornon-directional porosity. “Directional porosity” is achieved, forexample, with channels that extend in the flushing element.“Non-directional porosity” can be achieved with a porous refractorymaterial that has corresponding gas permeability.

Gas flushing devices can be installed into a refractory lining of ametallurgical melting vessel that forms a wall or the bottom of thevessel. However, they may also be realized in the bottom or a wallin-situ, for example, as described in EP 0 560 834 B1.

Gas flushing elements primarily serve for conducting gas. However, a gasflushing device of this type may also conduct gas/solid mixtures incertain instances.

The gases used may be inert gases, for example, when flushing ladles.However, it is also known to flush with oxygen, for example, in electricfurnaces.

All gas flushing/purging devices are subjected to significant wear,particularly a chemical/corrosive attack. This is the reason why thesegas purging devices need to be replaced regularly.

The left part of FIG. 1 shows a conventional gas purging device. Aso-called gas purging lance L is guided into the bottom region H of anelectric furnace from outside, wherein said lance is held on the outercasing A of the vessel with the aid of washers B and mounted by means ofa flange. Subsequently, a well nozzle S is placed over the lance L and amass is filled between the well nozzle and the lance. The well nozzle Sis subsequently walled in with bricks M and the bottom H is then linedwith a furnace mass.

Once the gas purging device is worn out (indicated with a broken line inFIG. 1), the entire purging device needs to be cleared. This leads tothe situation illustrated in the left part of FIG. 2. A new gas flushingdevice is subsequently installed as described above.

This method is very time-consuming and nearly the entire hearth mass ofthe bottom needs to be cleared, particularly up to the outer casing A.

Consequently, it is an object of the invention to develop a gas purgingdevice that can be replaced faster and cheaper when it is worn out.

The invention proposes to separate the parts of the gas purging devicethat are subject to particular wear, i.e., the parts of the gas flushingdevice that are situated adjacent to the molten metal or the partssituated at the gas outlet end, from the parts arranged upstreamthereof, i.e., in the direction of the gas inlet end.

When an exchange is required, individual parts of the gas purging devicemay remain and only the actually worn zones or worn parts are replaced.

According to another aspect, the actual flushing element is realized ina monolithic mass in the section that is situated adjacent to the wallof the melting vessel. This mass simplifies the alignment of theflushing element during the installation of the flusher. This mass canalso be cleared and replaced more easily when the flushing device istorn down. The mass may be arranged, in turn, in a permanent receptaclethat is not exchanged when the flusher (purging element) is replaced.

According to its most general embodiment, the invention pertains to agas purging device for metallurgical melting vessels with the followingcharacteristics:

a gas purging brick is arranged in an upper cylindrical receptacle withits end on the gas outlet side and in a lower cylindrical receptaclewith its adjacent section, and

an annular space provided at least between the lower receptacle and thegas purging brick is filled with a mass, wherein

the gas purging brick, the receptacles and the mass are made of arefractory ceramic material.

In this context, the term “cylindrical” merely refers to a body that isopen on opposite sections and serves for accommodating another body,wherein this term does not imply any other geometric restrictions.

The lower receptacle is not subjected to wear in the normal operatingstate and can be enclosed with refractory bricks or a refractory mass(hearth mass) that also remains as a permanent lining when a replacementis required. Its serves for receiving a refractory ceramic mass, forexample, a ramming mass, which simultaneously serves for adjusting thepurging element (gas purging brick) when it is aligned in the lowerreceptacle and embedded in the mass. The upper cylindrical receptacle issituated adjacent to and practically forms an extension of the lowerreceptacle (referred to the flow direction of a gas or the directiontoward the molten metal). This upper receptacle may have, for example, acircular inside cross section and encloses the purging device in a moreor less direct fashion such that it forms a mechanical guide as well asa protection against chemical attacks.

The gas purging element may be arranged in the upper receptacle (i.e.,on the “hot side”) flush or with slight clearance. It

may be fixed in the upper receptacle by means of an adhesive or mortar.

The gas purging brick usually extends over the entire length (height) ofthe upper and the lower receptacle. It may also protrude the upperreceptacle by a short distance (when mounted). The gas connection and,if applicable, a gas distribution chamber for distributing gas toindividual channels or pores are situated on the other end.

The flusher (gas purging element) may have a circular cross section.However, gas flushing elements in the shape of truncated cones or cuboidgeometries may also be utilized. When using a cuboid purging element,the upper receptacle accordingly has a rectangular cross section.

In this context, the term “cylindrical receptacle” should be understoodin the form of an enclosure for a certain length of the gas purgingelement regardless of its inside cross section. The outside crosssection may have an arbitrary shape.

At least one receptacle may be realized in the form of a pressed part.Pressed enclosure parts for the flushing element are particularly tightand consequently wear-resistant.

The purging element itself can be realized with directed or non-directedporosity. Purging elements with directed porosity are used, inparticular, when purging electric furnaces with oxygen. This can beachieved by realizing the purging element with several tubular channelsthat extend in the axial direction and consist, for example, of smallmetal or ceramic tubes. The purging element may be equipped with anadditional lance (separate gas supply for purging element and lance) orconsist merely of a lance lined with refractory material.

The length of the upper receptacle is determined in dependence on therespective application and the expected wear, namely because only theupper receptacle should be subsequently replaced.

According to one embodiment, the upper receptacle is at least as long asthe lower receptacle. However, the upper receptacle may be up tofour-times as long as the lower receptacle referred to the axialdirection of the flushing element, i.e., in the flow direction of thegas. For example, the upper receptacle is two-times to three-times aslong as the lower receptacle.

The upper receptacle may have a cross-sectional shape that makes itpossible to directly place the upper receptacle on the lower receptacle.However, the upper receptacle may also have a wall thickness thatcorresponds to the wall thickness of the refractory mass introducedbetween the flushing element and the lower receptacle as discussed belowin the description of the figures.

It usually suffices to realize the upper receptacle with an outsidecross section that is smaller than the outside cross section of thelower receptacle. This means that the gas purging device has a steppedcross section as shown in the right part of FIGS. 1, 2. However, itwould also be conceivable to realize embodiments, in which the upperreceptacle ends at a certain distance in front of the lower receptacleor protrudes into the lower receptacle.

The described gas purging device can be installed into the bottom or awall of a metallurgical melting vessel. The term “metallurgical meltingvessel” includes all crucibles for melting metal and for treating moltenmetal, respectively. The gas purging device consequently is alsosuitable for installation into the hearth bottom of an electric furnace,for example, an electric arc furnace.

Other characteristics of the invention are disclosed in the dependentclaims as well as the remaining application documents. This includes themulti-part design of one or both receptacles.

One embodiment of the invention is described below with reference to thefigures that respectively show a schematic section through theembodiment in the right part of FIGS. 1, 2.

The gas purging device comprises a total of four parts. A lowerreceptacle 10 is initially inserted during the lining process. Thisreceptacle is a pressed, refractory enclosure of annular shape.Subsequently, a purging brick 12 with directed porosity (channels 20) isinserted via the outer wall A through an opening 14 from below (fromoutside), and its section 12 u is centered in the lower receptacle 10 aswell as the region situated thereunder with the aid of a ramming mass.The gas outlet end 12 o of the purging element 12 protrudes the lowerreceptacle 10 and the mass 16, respectively. An upper receptacle 18 thatis also realized cylindrically analogous to the lower receptacle 10 isthen placed over the upper section 12 o of the gas purging element,wherein the upper receptacle has an inside cross section thatcorresponds to the outside cross section of the gas purging element 12.The upper receptacle 18 is aligned with the annular channel, filled withthe mass 16, between the lower receptacle 10 and the purging element 12.The upper receptacle 18 is twice as long as the lower receptacle 10. Thehearth mass H is ultimately introduced and the hearth bottom is formed.

In an alternative variation of the embodiment shown, the regionunderneath the lower receptacle 10 may also be equipped with mountingelements B analogous to the state of the art, for example, washers (asillustrated in the left part of FIGS. 1, 2) in order to fix the purgingelements 12 on the outer wall A of the melting vessel.

The time required for lining the gas purging device shown in FIGS. 1, 2is approximately one hour.

The time required for a lining process in accordance with the state ofthe art that is illustrated in the left part of FIGS. 1, 2 isapproximately 2.5 hours. Another advantage of the gas flushing deviceaccording to the invention can be seen in the fact that the lowerreceptacle 10 can remain when a replacement is required (FIG. 2). Inaddition, the zones of the hearth mass H that are situated adjacent tothe outer wall A can be largely preserved such that the requiredquantity of new hearth mass is reduced.

1. A gas purging device for metallurgical melting vessels with thefollowing characterstics: 1.1 a gas purging brick (12) is arranged in anupper cylindrical receptacle (18) with its end (12 o) on the gas outletside and in a lower cylindrical receptacle (10) with its adjacentsection (12 u), and 1.2 an annular space provided at least between thelower receptacle (10) and the gas purging brick (12) is filled with amass (16), wherein 1.3 the gas purging brick (12), the receptacles (10,18) and the mass (16) are made of a refractory ceramic material.
 2. Thegas purging device according to claim 1, the gas purging brick (12) ofwhich is arranged in the upper receptacle (18) flush or with slightclearance.
 3. The gas purging device according to claim 1, the gaspurging brick (12) of which extends over the entire height of the lowerand the upper receptacle (10, 18).
 4. The gas purging device accordingto claim 1, the gas purging brick (12) of which has a circular crosssection.
 5. The gas purging device according to claim 1, wherein atleast one receptacle (10, 18) is realized in the form of a pressed part.6. The gas purging device according to claim 1, the gas purging brick(12) of which has a directed porosity.
 7. The gas purging deviceaccording to claim 1, the gas purging brick (12) of which comprisesseveral small metal or ceramic tubes (20) that extend in the axialdirection and serve for achieving a directed porosity.
 8. The gaspurging device according to claim 1, the upper receptacle (18) of whichis at least as long as the lower receptacle (10).
 9. The gas purgingdevice according to claim 1, the upper receptacle (18) of which is1.1-times to 10-times as long as the lower receptacle (10).
 10. The gaspurging device according to claim 1, the upper receptacle (18) of whichis 2-times to 3-times as long as the lower receptacle (10).
 11. The gaspurging device according to claim 1, the upper receptacle (18) of whichhas an outside cross section that is larger than the inside crosssection of the lower receptacle (10).
 12. The gas purging deviceaccording to claim 1, wherein the upper receptacle (18) lies on thelower receptacle (10).
 13. The gas purging device according to claim 1,the upper receptacle (I 8) of which has an outside cross section that issmaller than the outside cross section of the lower receptacle (10). 14.The gas purging device according to claim 1, wherein the upperreceptacle (18) protrudes into the lower receptacle (10).
 15. The gaspurging device according to claim 1, the mass (16) of which is a rammingmass.
 16. The gas purging device according to claim 1, wherein at leastone of the receptacles (10, 18) comprises more than one part.
 17. Use ofa gas purging device according to claim 1, for installation in thebottom (H) of a metallurgical melting vessel.
 18. Use of a gas purgingdevice according to claim 1, for installation in the hearth bottom (H)of an electric furnace.